The present invention relates to copolyester resin composition which has good physical properties and biodegradability and a process for preparing and/or producing the same which is suitable for various applications, such as films, moldings, and fiber. More particularly, the present invention have solved a problem of poor physical properties, especially tensile strength and tear strength, so it can be used in many practical uses including packaging film and trash bags.
Many aliphatic polyester resin compositions have been published in the literature, and they completely biodegrade in the environment. But they have difficulty in commercializing because of high cost, poor physical properties and inferior processability comparing to the conventional polymers such as polyethylene, polypropylene and polystyrene.
The typical polyester resin used for various products including textures, fibers, moldings, formings, films, etc, is a high molecular weight aromatic polyester resin produced by the polycondensation reaction of terephthalic acid with ethylene glycol, or terephthalic acid with 1,4-butanediol. The high molecular weight polyester resin is a polymer having a number average molecular weight of over 10,000. Such aromatic polyester resins are not degradable naturally so it is a serious, worldwide of environmental concern.
Otherwise, the aliphatic polyester resins are known as being biodegradable (J.Macromol. Sci.-Chem., A23(3), pp.393-409 (1986)). They have a variety of usage in the medical and agricultural fields, and other applications are being developed.
However, the conventional aliphatic polyester resin has a low melting point and a high melt index, because of the structure of the main chain and the crystallinity thereof, and having low heat resistance and unsatisfactory mechanical properties, the usage of this polymer material has been limited. In order to utilize this aliphatic polyester resin, it should have a number average molecular weight of more than 30,000. However, it is difficult to manufacture the aliphatic polyester resins having a number average molecular weight of more than 15,000 using the conventional polycondensation reaction system because further growth reaction is surpassed by decomposition reaction due to the poor heat stability of aliphatic polyesters.
In order to solve this problem, Korean Laid-Open Patent No. 95-758 discloses the process of preparing high molecular weighted aliphatic polyester resin having a number average molecular weight of more than 30,000, by controlling the reaction temperature, the degree of vacuum and the amount of catalyst. However, this aliphatic polyester resin has poor processability because of its low weight average molecular weight and low heat stability.
In another method, Korean Laid-Open Patent No. 95-114171 discloses the process of preparing the high molecular weighted aliphatic polyester resin by introducing monomer which containing poly(at least three)-functional groups, where the recommended functional group is hydroxy group(xe2x80x94OH) or carboxylic group(xe2x80x94COOH). According to this process, by introducing the monomer, the reaction time can be reduced and the processability of the resin can be enhanced by broadening molecular weight distribution. However, the utilization of the polyester resin thereof is very difficult because the physical property such as a tensile strength is poor due to the increased amount of low molecular weight portions. Furthermore, it is difficult to control the reaction for preparing the polyester resin, because the polyester resin easily becomes a gel type.
In yet another process for increasing the molecular weight of the aliphatic polyester resin, Korean Laid-Open Patent No. 95-25072 discloses the high molecular weighted aliphatic polyester resin produced by using isocyanate as a coupling agent reacting to an aliphatic polyester resin having a number average molecular weight of from 15,000 to 20,000, which is produced by de-hydration reaction or de-glycol reaction of (1) an aliphatic (including cyclic type), and (2) an aliphatic (including cyclic type) dicarboxylic acid (or an acid anhydride thereof), and a little of (3) monomer of polyhydric alcohol or polyhydric carboxylic acid (or acid anhydride thereof). According to the application, the aliphatic polyester resin has a number average molecular weight of from 20,000 to 70,000. However, this process requires more time for the reaction which leads to the poor production yield. And the isocyanate used as a coupling agent to increase the molecular weight is harmful to the human body so it needs to be handled carefully.
In yet another process for increasing the molecular weight of the aliphatic polyester resin, U.S. Pat. No. 5,843,573 discloses the high molecular weighted aliphatic polyester resin produced by using twin-screw extruder. However this process is very complicated and requires more time for the reaction.
In yet another process for increasing the molecular weight of the aliphatic polyester resin, World Patent WO9503347A1 discloses the high molecular weighted aliphatic polyester resin produced by using diethylene glycol as a glycol ingredient. However this process requires more time for the reaction, and the product is not desirable for practical use because of its low melting point and poor physical properties.
In the conventional process as mentioned above, it has been used to introduce a coupling agent like an isocyanate or a monomer such as a polyhydric alcohol or polyhydric carboxylic acid. These conventional processes have many problems such as low production yields, poor physical properties and/or poor processability.
The present invention provides a copolyester resin composition which has good physical properties, biodegradability and processability and a process for preparing and/or producing the same. To improve the biodegradability and physical properties of the copolyester, the present invention applied multi-stage reaction step, and copolyester resin having number average molecular weight of from 30,000 to 70,000, weight average molecular weight of from 100,000 to 600,000, melting point of from 55xc2x0 C. to 120xc2x0 C., and melt index of from 0.1 to 30 g/10 minute (190xc2x0 C., 2,160 g) is obtained. The processability and physical properties of the copolyester resin of the present invention has been greatly enhanced by incorporating (i) an xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d having number average molecular weight of from 300 to 30,000 and the contiguous repeating unit of aromatic group in the dicarboxylic acid position of xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d is less than 5. Thus it can be processed by using the conventional processing equipment for polyethylene and polypropylene without any modification.
To solve the above mentioned problems, the present inventors applied multi-stage reaction step. The copolyester resin composition according to the present invention would be described in detail hereinafter.
In the first reaction step, the oligomer-like substances (hereinafter, referred to as xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d) having number average molecular weights of from 300 to 30,000 and the contiguous repeating unit of aromatic group in the dicarboxylic acid position of xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d is less than 5, is obtained through one or a plurality of condensation, esterification and ester-exchange reaction with three ingredients;
(a) one or a plurality of aromatic dicarboxylic acid (or an acid anhydride thereof) which containing aromatic group in the molecule, selected from dimethyl terephthalate, terephthalic acid, phthalic acid, phthalic anhydride, isophthalic acid, 4-methylphthalic acid, 4-methylphthalic anhydride, dimethyl phthalate;
(b) one or a plurality of aliphatic (including cyclic type) dicarboxylic acid (or an acid anhydride thereof) ingredient selected from succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid; and
(c) one or a plurality of aliphatic (including cyclic type) glycol selected from ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,2-octanediol, 1,8-octanediol, 1,9-nonanediol, 1,2-decanediol, 1,10-decanediol, decamethylene glycol
Next, in the second reaction step, with the existence of (i) an xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d which was produced in the first reaction step, from 0.1 wt % to 30 wt %, (ii) one or a plurality of aliphatic (including cyclic type) dicarboxylic acid (or an acid anhydride thereof) ingredient selected from succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, from 40 wt % to 71 wt %, and (iii) one or a plurality of aliphatic (including cyclic type) glycol selected from ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,2-octanediol, 1,8-octanediol, 1,9-nonanediol, 1,2-decanediol, 1,10-decanediol, decamethylene glycol, from 29 wt % to 60 wt %, are added, and one or a plurality of esterification and ester-exchange reaction are performed and thus obtain the polymeric resin.
Finally, in the third reaction step, by polycondensing the polymeric resin which was produced in the second reaction step, a copolyester with number average molecular weight of from 30,000 to 70,000, weight average molecular weight of from 100,000 to 600,000, melting point of from 55xc2x0 C. to 120xc2x0 C., and melt index of from 0.1 to 30 g/10 minute (190xc2x0 C., 2,160 g) is obtained.
To describe in more detail about the copolyester resin composition of the present invention, in the first reaction step, (i) an xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d having number average molecular weights of from 300 to 30,000 and the contiguous repeating unit of aromatic group in the dicarboxylic acid position of xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d is less than 5, are obtained by performing reactions which are selected from at least one of the following reactions; condensation reaction, or an esterification reaction, or an ester-exchange reaction, with (a) one or a plurality of aromatic dicarboxylic acid (or an acid anhydride thereof) which containing aromatic group in the molecule, including dimethyl terephthalate and terephthalic acid; (b) one or a plurality of aliphatic (including cyclic type) dicarboxylic acid (or an acid anhydride thereof) ingredient including succinic acid; and (c) one or a plurality of aliphatic (including cyclic type) glycol selected from at least one of 1,4-butanediol and ethylene glycol, preferably one of {circle around (1)} succinic acid alone; ethylene glycol alone or mixture of ethylene glycol and other glycol (C3-C10 alkylene, C4-C10 cycloalkylene); aromatic dicarboxylic acid (dimethyl terephthalate, terephthalic acid), {circle around (2)} succinic acid alone; 1,4-butanediol alone or mixture of 1,4-butanediol and other glycol (C2-C3 and C5-C10 alkylene, C4-C10 cycloalkylene); aromatic dicarboxylic acid (dimethyl terephthalate, terephthalic acid), {circle around (3)} succinic acid alone or mixture of succinic acid and other dicarboxylic acid (C3-C10 alkylene, C4-C10 cycloalkylene); ethylene glycol alone; aromatic dicarboxylic acid (dimethyl terephthalate, terephthalic acid), {circle around (4)} succinic acid alone or mixture of succinic acid and other dicarboxylic acid (C3-C10 alkylene, C4-C10 cycloalkylene); 1,4-butanediol alone; aromatic dicarboxylic acid (dimethyl terephthalate, terephthalic acid), {circle around (5)} succinic acid alone or mixture of succinic acid and other dicarboxylic acid (C3-C10 alkylene, C4-C10 cycloalkylene); ethylene glycol alone or mixture of ethylene glycol and other glycol (C3-C10 alkylene, C4-C10 cycloalkylene); aromatic dicarboxylic acid (dimethyl terephthalate, terephthalic acid), {circle around (6)} succinic acid alone or mixture of succinic acid and other dicarboxylic acid (C3-C10 alkylene, C4-C10 cycloalkylene); 1,4-butanediol alone or mixture of 1,4-butanediol and other glycol (C2-C3 and C5-C10 alkylene, C4-C10 cycloalkylene); aromatic dicarboxylic acid (dimethyl terephthalate, terephthalic acid).
Next, in the second reaction step, with the existence of from 0.1 wt % to 30 wt % of (i) an xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d which was produced in the first reaction step, (ii) one or a plurality of aliphatic (including cyclic type) dicarboxylic (or an acid anhydride thereof) ingredient including succinic acid; and (iii) one or a plurality of aliphatic (including cyclic type) glycol selected from at least one of 1,4-butanediol and ethylene glycol, preferably one of {circle around (1)} succinic acid alone; ethylene glycol alone or mixture of ethylene glycol and other glycol (C3-C10 alkylene, C4-C10 cycloalkylene), {circle around (2)} succinic acid alone; 1,4-butanediol alone or mixture of 1,4-butanediol and other glycol (C2-C3 and C5-C10 alkylene, C4-C10 cycloalkylene), {circle around (3)} succinic acid alone or mixture of succinic acid and other dicarboxylic acid (C3-C10 alkylene, C4-C10 cycloalkylene); ethylene glycol alone, {circle around (4)} succinic acid alone or mixture of succinic acid and other dicarboxylic acid (C3-C10 alkylene, C4-C10 cycloalkylene); 1,4-butanediol alone, {circle around (5)} succinic acid alone or mixture of succinic acid and other dicarboxylic acid (C3-C10 alkylene, C4-C10 cycloalkylene); ethylene glycol alone or mixture of ethylene glycol and other glycol (C3-C10 alkylene, C4-C10 cycloalkylene), {circle around (6)} succinic acid alone or mixture of succinic acid and other dicarboxylic acid (C3-C10 alkylene, C4-C10 cycloalkylene); 1,4-butanediol alone or mixture of 1,4-butanediol and other glycol (C2-C3 and C5-C10 alkylene, C4-C10 cycloalkylene), are added, and one or a plurality of esterification and ester-exchange reaction are performed and thus obtain the polymeric resin after water or methanol is extracted.
The present invention provides a process for preparing and/or producing above mentioned copolyester resin comprising three reaction steps which are described below in detail.
In the first reaction step, (i) an xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d having number average molecular weights of from 300 to 30,000 and the contiguous repeating unit of aromatic group in the dicarboxylic acid position of xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d is less than 5, is obtained by performing reactions which are selected from at least one of the following reactions; condensation reaction, or an esterification reaction, or an ester-exchange reaction, at the temperature of from 160xc2x0 C. to 240xc2x0 C., with (a) one or a plurality of aromatic dicarboxylic acid (or an acid anhydride thereof) which containing aromatic group in the molecule including dimethyl terephthalate and terephthalic acid, (b) one or a plurality of aliphatic (including cyclic type) dicarboxylic acid (or an acid anhydride thereof) ingredient including succinic acid, and (c) one or a plurality of aliphatic (including cyclic type) glycol selected from at least one of 1,4-butanediol and ethylene glycol, and the produced water or methanol is extracted. If the reaction temperature is lower than 160xc2x0 C., the produced water or methanol cannot easily extracted. If the reaction temperature is higher than 240xc2x0 C., the reactant can be decomposed due to thermal degradation.
To describe in more detail, at first, (a) one or a plurality of aromatic dicarboxylic acid (or an acid anhydride thereof) which containing aromatic group in the molecule, including dimethyl terephthalate and terephthalic acid, and (c) one or a plurality of aliphatic (including cyclic type) glycol selected from at least one of 1,4-butanediol and ethylene glycol, are added and react to produce water or methanol by performing reactions selected from at least one of the following reaction; condensation reaction, or esterification reaction, or ester-exchange reaction, at the temperature of from 180xc2x0 C. to 220xc2x0 C. where the aromatic dicarboxylic acid become activated to react with the aliphatic glycol. Then after the produced water or methanol is extracted thereof, at the temperature of from 160xc2x0 C. to 180xc2x0 C. where the aromatic dicarboxylic acid become deactivated to react with the aliphatic glycol, (b) one or a plurality of aliphatic (including cyclic type) dicarboxylic acid (or an acid anhydride thereof) ingredient including succinic acid, is added to produce (i) an xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d having number average molecular weights of from 300 to 30,000 and the contiguous repeating unit of aromatic group in the dicarboxylic acid position of xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d is less than 5, by performing reactions which are selected from at least one of the following reactions; condensation reaction, or esterification reaction, or ester-exchange reaction. Because the contiguous repeating unit of aromatic group in the dicarboxylic acid position of xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d is less than 5, the biodegradability of the copolyester does not affected. During the reaction process, the chemical reaction is represented by the following formula (I), wherein terephthalic acid is employed for the (a) aromatic dicarboxylic acid (or an acid anhydride thereof) which containing aromatic group in the molecule, succinic acid is employed for the (b) aliphatic (including cyclic type) dicarboxylic acid (or an acid anhydride thereof) ingredient, and 1,4-butanediol is employed for the (c) aliphatic (including cyclic type) glycol. 
The product A) and/or B) from the reaction according to the formula (I) distribute randomly in the xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d, and can be represented by the following formula (II). 
Wherein the number average molecular weight of xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d is from 300 to 30,000 and the contiguous repeating unit of aromatic group in the dicarboxylic acid position of xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d is less than 5.
To produce (i) an xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d having number average molecular weight of from 300 to 30,000 and the contiguous repeating unit of aromatic group in the dicarboxylic acid position of xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d is less than 5, in the first reaction step, for 1.0 mole of total dicarboxylic acid (sum of (a) and (b)) which is added in the first reaction step, the mole ratio of (c) aliphatic (including cyclic type) glycol is from 1.1 mole to 1.5 mole. And for dicarboxylic acids ingredient which are added in the first reaction step, the mole ratio of aromatic component to aliphatic component is in the range from 0.2:0.8 to 0.8:0.2. If the mole ratio is less than 0.2:0.8, the reactivity decreases and the copolyester resin has poor physical properties and color. If the mole ratio is higher than 0.8:0.2, the rate of biodegradation decreases. And the preferable mole ratio among (a) aromatic dicarboxylic acid (or an acid anhydride thereof): (b) aliphatic (including cyclic type) dicarboxylic acid (or an acid anhydride thereof): (c) aliphatic (including cyclic type) glycol is 0.45:0.55:1.35.
Then, in the second reaction step, with the existence of (i) an xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d which was produced in the first reaction step, (ii) one or a plurality of aliphatic (including cyclic type) dicarboxylic acid (or an acid anhydride thereof) ingredient including succinic acid, and (iii) one or a plurality of aliphatic (including cyclic type) glycol selected from at least one of 1,4-butanediol and ethylene glycol are added, and at the temperature of from 200xc2x0 C. to 220xc2x0 C., one or a plurality of esterification and ester-exchange reaction are performed. After the produced water or methanol is extracted, polymeric resin is obtained. The amount of the (i) xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d ranges from 0.1 wt % to 30 wt %. If the amount of the (i) xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d is less than 0.1 wt %, not only the reaction time becomes longer but also the physical properties become poorer. If the amount of the (i) xe2x80x9caromatic-aliphatic prepolymersxe2x80x9d is more than 30 wt %, the rate of biodegradation becomes slow and the melting point gets lower so it is difficult to process by plastic processing equipment.
Finally, in the third reaction step, by polycondensing the polymeric resin which was produced in the second reaction step, at the temperature of from 210xc2x0 C. to 270xc2x0 C. and 0.005xcx9c10 Torr, a copolyester resin with number average molecular weight of from 30,000 to 70,000, weight average molecular weight of from 100,000 to 600,000, melting point of from 55xc2x0 C. to 120xc2x0 C., and melt index of from 0.1 to 30 g/10 minute (190xc2x0 C., 2,160 g) is obtained.
At the start of and/or the end of the esterification or ester-exchange reaction in the first and second reaction step, catalyst alone or mixture of a plurality of catalysts can be added, wherein the amount of the catalyst(s) is preferably in the range of from 0.02 wt % to 2.0 wt % of total reactants. If the amount of catalyst employed is less than 0.02 wt %, it takes long time to extract the theoretical amount of water, methanol or glycol, or it is impossible to extract. If the amount of the catalyst employed is more than 2.0 wt %, the color of the product is poor even though the theoretical amount of water, methanol or glycol is easily extracted. The catalysts are selected from one or a plurality of the metallic compounds consisting Ti, Ge, Zn, Fe, Mn, Co, and Zr, preferably, an organic metallic compound consisting titanate, antimonate or tin oxide, more preferably, selected from one or a plurality of tetrabutyl titanate, calcium acetate, antimony trioxide, dibutyltin oxide, zinc acetate, antimony acetate, antimony glycolate, tetrapropyl titanate.
Additionally, at the start of and/or the end of the esterification or ester-exchange reaction in the first and second reaction step, a stabilizer should be added wherein the amount of the stabilizer employed preferably ranges from 0.02 wt % to 2.0 wt %. If the amount of the stabilizer used is less than 0.02 wt %, the effect of the stabilizer is not sufficient and the color of the copolyester is yellow or brown. If the amount of the stabilizer exceeds 2.0 wt %, the time required for the reaction is extended and the product would not have high molecular weight. Therefore, the preferable amount of the stabilizer is about 0.22 wt %, and the stabilizer used is at least one or a plurality selected from phosphatic stabilizers consisting trimethyl phosphate, phosphoric acid and triphenyl phosphate.
The copolyester in the present invention is obtained by performing the multi-stage reaction step, and the number average molecular weight is from 30,000 to 70,000, the weight average molecular weight is from 100,000 to 600,000, the melting point is from 55xc2x0 C. to 120xc2x0 C., and the melt index is from 0.1 to 30 g/10 minute (190xc2x0 C., 2,160 g). Because of the enhanced physical properties and processability of the copolyester resin according to the present invention, it is possible to use for packaging film and trash bags.
Having this invention described in general, a further understanding can be obtained with reference to certain specific examples which are provided hereinafter for the purpose of illustration only and are not intended to be limited unless otherwise specified.